Non-volatile memory devices and methods of forming the same

ABSTRACT

A non-volatile memory device includes an upwardly protruding fin disposed on a substrate and a control gate electrode crossing the fin. A floating gate is interposed between the control gate electrode and the fin and includes a first storage gate and a second storage gate. The first storage gate is disposed on a sidewall of the fin, and the second storage gate is disposed on a top surface of the fin and is connected to the first storage gate. A first insulation layer is interposed between the first storage gate and the sidewall of the fin, and a second insulation layer is interposed between the second storage gate and the top surface of the fin. The second insulation layer is thinner than the first insulation layer. A blocking insulation pattern is interposed between the control gate electrode and the floating gate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 2004-80459, filed on Oct. 8, 2004 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor devices and methods of forming the same. More specifically, the present invention is directed to non-volatile memory devices and methods of forming the same.

2. Description of Related Art

Non-volatile memory devices retain their stored data even when their power supplies are interrupted. Representative non-volatile memory devices are flash memory devices. Conventionally, flash memory devices have a stacked gate structure that is advantageous in high integration density. A flash memory cell of a typical stacked gate structure is disclosed in Korean Patent Application No. 10-0396698, which will now be described with reference to FIG. 1.

As illustrated in FIG. 1, a control gate electrode 5 is disposed on a semiconductor substrate 1. A floating gate 3 is interposed between the control gate electrode 5 and the semiconductor substrate 1. A tunnel oxide layer 2 is interposed between the floating gate 3 and the semiconductor substrate 1. A dielectric layer 4 is interposed between the control gate electrode 5 and the floating gate 3. The floating gate 3 is electrically isolated by the tunnel oxide layer 2 and the dielectric layer 4.

The conventional flash memory cell stores data of logic “1” or “0” based on the amount of charges stored in the floating gate 3.

Various issues arise as conventional flash memory cells are further developed for higher integration. For example, the width of a channel region below the floating gate 3 tends to decrease, so that the turn-on current of the flash memory cell may decrease sharply to increase the sensing margin of the flash memory device. Further, as the overlap area of the floating gate 3 and the control gate 5 decreases, the coupling ratio of the flash memory cell may decrease to increase the operation voltage of the flash memory cell. Due to the increase in the operation voltage, the power consumption of a device increases and a boundary portion of the substrate 1 may damage, causing the reliability of the flash memory cell to degrade.

SUMMARY OF THE INVENTION

A feature of the present invention is to provide a non-volatile memory device capable of increasing the turn-on current within a limited area and a method of forming the same.

Another feature of the present invention is to provide a non-volatile memory device capable of increasing the coupling ratio within a limited area and a method of forming the same.

Another feature of the present invention is to provide a non-volatile memory device capable of decreasing the operation voltage within a limited area and a method of forming the same.

Another feature of the present invention is to provide a non-volatile memory device capable of optimizing the threshold voltage of a cell and a method of forming the same.

A non-volatile memory device is provided which includes an upwardly protruding fin disposed on a semiconductor substrate and a control gate crossing the fin. A floating gate is interposed between the control gate electrode and the fin. The floating gate includes a first storage gate and a second storage gate. The first storage gate is disposed on a sidewall of the fin, and the second storage gate is disposed on a top surface of the fin and is connected to the first storage gate. A first insulation layer is interposed between the first storage gate and the sidewall of the fin, and a second insulation layer is interposed between the second storage gate and the top surface of the fin. The second insulation layer is thinner than the first insulation layer. A blocking insulation pattern is interposed between the control gate electrode and the floating gate.

In some embodiments, the first storage gate is made of first doped polysilicon and the second storage gate is made of second doped polysilicon. An impurity concentration of the first doped polysilicon may be different from that of the second doped polysilicon. Preferably, the impurity concentration of the first doped polysilicon is higher than that of the second doped polysilicon. At a write or erase operation, the second insulation layer has a thickness sufficient to allow tunneling of charges and the first insulation layer has a thickness sufficient to suppress tunneling of charges. An upper corner of the fin may be rounded. The first and second insulation layer may be made of thermal oxide. An outer sidewall of the first storage gate may be aligned to a sidewall of the second storage gate. The non-volatile memory device may further include a filling insulation pattern disposed over the substrate to surround a lower sidewall of the fin. Alternatively, the non-volatile memory device may further include a buried insulation layer disposed over the substrate. In this case, the fin is disposed on the buried insulation layer.

According to a method of forming a non-volatile device, an upwardly protruding fin is formed on a substrate. A first insulation layer and a first storage pattern are sequentially stacked on a sidewall of the fin. A second insulation layer and a second storage pattern are sequentially formed on a top surface of the fin. The second insulation layer is thinner than the first insulation layer, and the second storage pattern is connected to the first storage pattern. A blocking insulation layer and a control gate conductive layer are sequentially formed on the substrate. The control gate conductive layer, the blocking insulation layer, the first storage pattern, and the second storage pattern are successively patterned to form a floating gate including the first and second storage gates, a block insulation pattern, and a control gate electrode.

In some embodiments, the first storage gate is made of first doped polysilicon and the second storage gate is made of second doped polysilicon. An impurity concentration of the first doped polysilicon is different from that of the second doped polysilicon. Preferably, the impurity concentration of the first doped polysilicon is higher than that of the second doped polysilicon. Forming the first insulation layer, the first storage pattern, the second insulation layer, and the second storage pattern may include forming a first insulation layer on a top surface and a sidewall of the fin. A first storage layer is formed on the first insulation layer to surround the sidewall of the fin. In this case, the first insulation layer formed on the top surface of the fin is exposed. The exposed first insulation layer is selectively removed to expose the top surface of the fin. A second insulation layer is selectively formed on the exposed top surface of the fin. A second storage layer is formed to cover the second insulation layer and to be connected to the first storage layer. The second storage layer and the first storage layer are successively patterned to form the second and first storage patterns.

In some embodiments, exposing the top surface of the fin to form the second insulation may include forming an oxidation barrier layer on an entire surface of a substrate having the exposed first insulation layer. The oxidation barrier layer is patterned to expose a predetermined area of the exposed first insulation layer. Using the patterned oxidation barrier layer as a mask, the first insulation layer is etched to expose the top surface of the fin. The substrate is thermally oxidized to form the second insulation layer. The patterned oxidation barrier layer is then removed.

In some embodiments, exposing the top surface of the fin to form the second insulation layer may include recessing the first storage layer to be shorter than the exposed top surface of the first insulation layer. An oxidation barrier layer is formed on a substrate to fill the recessed area. The oxidation barrier layer is planarized until the first insulation layer is exposed. Using the planarized oxidation barrier layer as an etch mask, the exposed first insulation layer is etched to expose the top surface of the fin. The substrate is thermally oxidized to form the second insulation layer. The planarized oxidation barrier layer is then removed.

In some embodiments, at a write or erase operation, the second insulation layer has a thickness sufficient to allow tunneling of charges and the first insulation layer has a thickness sufficient to suppress tunneling of charges.

In some embodiments, an upper corner of the fin may be rounded. In this case, forming the fin may include forming a mask pattern on a predetermined area of the substrate. A substrate having the mask pattern is thermally oxidized to form a sacrificial thermal oxide layer including a bird's beak below the edge of a lower portion of the mask pattern. Using the mask pattern as an etch mask, the sacrificial oxide layer and the substrate are successively anisotropically etched to form the fin and to remove the mask pattern and the bird's beak.

In some embodiments, the method further includes forming a filling insulation pattern on the substrate to surround a lower sidewall of the fin.

In some embodiments, the substrate may be a SOI substrate including a handling substrate, a buried insulation layer, and a device layer, which are stacked in the order named. The method may include patterning the device layer to form the fin on the buried insulation layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flash memory cell of a conventional stacked gate structure.

FIG. 2A is a top plan view of a non-volatile memory device according to an embodiment of the present invention.

FIG. 2B and FIG. 2C are cross-sectional views taken along lines I-I′ and II-II′ of FIG. 2A, respectively.

FIG. 3A through FIG. 9A are top plan views for explaining a method of forming a non-volatile memory device according to an embodiment of the present invention.

FIG. 3B through FIG. 9B are cross-sectional views taken along lines III-III′ of FIG. 3A through FIG. 9A, respectively.

FIG. 3C through FIG. 9C are cross-sectional views taken along lines IV-IV′ of FIG. 3A through FIG. 9A, respectively.

FIG. 10A through FIG. 12A are top plan views for explaining a method of selectively forming an insulation layer on a top surface of a fin, in the method of forming the non-volatile memory device according to an embodiment of the present invention.

FIG. 10B through FIG. 12B are cross-sectional views taken along lines V-V′ of FIG. 10A through FIG. 12A, respectively.

FIG. 10C through FIG. 12C are cross-sectional views taken along lines VI-VI′ of FIG. 10A through FIG. 12A, respectively.

FIG. 13A is a cross-sectional view showing a modified version of the non-volatile memory device according to an embodiment of the present invention.

FIG. 13B is a cross-sectional view taken from a direction VII-VII′ of FIG. 13A.

FIG. 14A and FIG. 15A are cross-sectional views for explaining a method of forming the modified version of the non-volatile memory device according to an embodiment of the present invention.

FIG. 14B and FIG. 15B are cross-sectional views taken from directions VIII-VIII′ of FIG. 14A and FIG. 15A, respectively.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. In the drawings, the height of layers and regions are exaggerated for clarity. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Like numbers refer to like elements throughout.

FIG. 2A is a top plan view of a non-volatile memory device according to an embodiment of the present invention. FIG. 2B and FIG. 2C are cross-sectional views taken along lines I-I′ and II-II′ of FIG. 2A, respectively.

As illustrated in FIG. 2A, FIG. 2B, and FIG. 2C, a non-volatile memory device includes a fin 106 disposed on a semiconductor substrate (hereinafter briefly referred to as “substrate”) 100. The fin 106 protrudes upwardly. The substrate 100 may be a bulk substrate. Preferably, an upper corner of the fin 106 is rounded so as to prevent concentration of an electric field. The fin 106 may be made of the same material as the substrate 100. A filling insulation pattern 108 is disposed on the substrate 100 to surround a lower sidewall of the fin 106. The filling insulation pattern 108 may be made of silicon oxide, particularly, high-density plasma silicon oxide or SOG of a superior gap-fill property. The filling insulation pattern 108 may act as a device isolation layer to isolate adjacent devices.

A control gate electrode 126 a is disposed over the substrate 100 to cross the fin 106. The control gate electrode 126 a is disposed on the filling insulation pattern 108. A floating gate 122 a is interposed between the control gate electrode 126 a and the fin 106. The floating gate 122 a includes first storage gate 112 c and a second storage gate 120 b. The first storage gate 112 c is disposed on a sidewall of the fin 106 below the control gate electrode 126 a, and the second storage gate 112 c is disposed on the top surface of the fin 106 below the control gate electrode 126 a. The second storage gate 120 b is electrically connected to the first storage gate 112 c. Particularly, the second storage gate 120 b extends laterally to be connected to the top surface of the first storage gate 112 c.

Specifically, a pair of the first storage gates 112 c are disposed on both sidewalls of the fin 106 below the control gate electrode 126 a, respectively. The second storage gate 120 b is disposed on the top surface of the fin 106 and extends in both side directions to be connected to top surfaces of the pair of the first storage gates 112 c. The floating gate 122 a includes the pair of the first storage gates 112 c and the second storage gate 120 b.

An outer sidewall of the first storage gate 112 c is aligned to a sidewall of the second storage gate 120 b. As illustrated in FIG. 2B, a contact face (i.e., the top surface of the first storage gate) 112 c) of the first and second storage gates 112 c and 120 b may be taller than the top surface of the fin 106. Alternatively, the contact face of the first and second storage gates 112 c and 120 b may be as tall as the top surface of the fin 106.

A first insulation layer 110 is interposed between the first storage gate 112 c and the sidewall of the fin 106, and a second insulation layer 118 is interposed between the second storage gate 120 b and the top surface of the fin 106. A blocking insulation pattern 124 a is interposed between the floating gate 122 a and the control gate electrode 126 a. An impurity doping layer 128 is disposed on the fin 106 of opposite sides adjacent to the control gate electrode 126 a to act as a source/drain region.

The second insulation layer 118 is thinner than the first insulation layer 110. Preferably, at a write or erase operation, the second insulation layer 118 is thin enough to allow tunneling of charges and the first insulation layer 110 is thick enough to suppress tunneling of charges. Thus, at a write or erase operation, charges may be tunneled only through the second insulation layer 118 disposed on the top surface of the fin 106. That is, only the second insulation layer 118 functions as a tunnel insulation layer.

A channel region is defined at the fin 106 below the floating gate 122 a. Since the channel region includes a vertical channel region defined at both sidewalls of the fin 106 and a horizontal channel region defined at the top surface of the fin 106, a width of the channel region increases within a limited area. This leads to an increase in the turn-on current, so that the sensing margin of the non-volatile memory device increases. As a result, the operation voltage drops, which leads to a non-volatile memory device of lower power consumption.

Due to the thick first insulation layer 110 disposed on both sides of the fin 106, the capacitance between the first storage gate 112 c and the fin 106 decreases. That is, the capacitance between the floating gate 122 a and the fin 106 decreases. The floating gate 122 a has a 3-dimensional structure to cover the top surface and both sidewalls of the fin 106, and the control gate electrode 126 a cover the top surface and an outer sidewall of the floating gate 122 a. Therefore, an overlap area of the floating gate 122 a and the control gate electrode 126 a increase. Since this leads to increase in the capacitance between the floating gate 122 a and the control gate electrode 126 a, the capacitance between the floating gate 122 a and the control gate electrode 126 a increases. The capacitance between the floating gate 122 a and the fin 106 decreases while the capacitance between the floating gate 122 a and the control gate electrode 126 a increases, leading to an increase in the coupling ratio of a non-volatile memory cell. Thus, the operation voltage of the non-volatile memory cell decreases, leading to a non-volatile memory device of lower power consumption.

The control gate electrode 126 a is made of a conduction material. That is, the control gate electrode 126 a may be made of one selected from the group consisting of, for example, doped polysilicon and metal silicide (e.g., tungsten silicide, cobalt silicide, nickel silicide and titanium silicide), conductive metal nitride (e.g., titanium nitride and tantalum nitride), metal (e.g., tungsten and molybdenum), and combinations thereof. The blocking insulation pattern 124 a may be made of oxide-nitride-oxide (ONO). Alternatively, the blocking insulation pattern 124 a may include a high-k dielectric layer having a higher dielectric constant than the blocking insulation pattern 124 a. The blocking insulation pattern 124 a may include, for example, a metal oxide layer (e.g., aluminum oxide layer or hafnium oxide layer) that is a high-k dielectric layer. Preferably, the first and second insulation layers 110 and 118 are made of silicon oxide having a superior characteristic, for example, thermal oxide.

Preferably, the floating gate 122 a is made of first doped polysilicon and the second floating gate 112 is made of second doped polysilicon. Thus, the first and second storage gates 112 c and 120 b may be made of different doped polysilicons to optimize the characteristics of the non-volatile memory cell, particularly, the threshold voltage.

Since the first and second storage gates 112 c and 120 b are electrically interconnected, the first and second doped polysilicons are doped with the same impurities. An impurity concentration of the first doped polysilicon may be different from that of the second doped polysilicon. Preferably, the impurity concentration of the first doped polysilicon is higher than that of the second doped polysilicon. Therefore, a non-volatile memory device having a uniform threshold voltage throughout the channel region (e.g., the vertical and horizontal channel regions) is made.

Since the thickness of the first insulation layer 110 is different from that of the second insulation layer 118, threshold voltages of the vertical channel region and the horizontal channel region may be different from each other. Since the first insulation layer 110 is thicker than the second insulation layer 118, an absolute value of the vertical channel region may be greater than that of the horizontal channel region. In this regard, an impurity concentration of the first storage gate 112 c increases relatively to enable a threshold voltage of the horizontal channel region to rise. Therefore, a uniform threshold voltage is achieved at the entire area of the channel region. As a result, when the non-volatile memory cell is sensed, the entire area of the channel region is simultaneously turned on to enhance the operating speed of the non-volatile memory device.

Preferably, the impurities of the first and second doped polysilicons have the same type as the impurities of the impurity doping layer 128. Further, the type of the impurities of the first and second doped polysilicons may be different from that of the impurities of the channel region.

A method of forming a non-volatile memory device according to the present invention will now be described more fully hereinafter.

FIG. 3A through FIG. 9A are top plan views for explaining a method of forming a non-volatile memory device according to an embodiment of the present invention. FIG. 3B through FIG. 9B are cross-sectional views taken along lines III-III′ of FIG. 3A through FIG. 9A, respectively. FIG. 3B through FIG. 9B are cross-sectional views taken along lines IV-IV′ of FIG. 3A through FIG. 9A, respectively.

Referring to FIG. 3A, FIG. 3B, and FIG. 3C, a mask pattern 102 is formed on a predetermined region of a substrate 100. The substrate 100 may be a bulk substrate. The mask pattern 102 serves to prevent oxidation caused by a thermal oxidation process and is made of a material having an etch selectivity with respect to a thermal oxide layer and the substrate 100. The mask pattern 102 may be, for example, a single layer of silicon nitride or a multiple layer of silicon oxide/silicon nitride.

A substrate 100 including the mask pattern 102 is thermally oxidized to form a sacrificial thermal oxide layer 104. A bird's beak 105, which is an extending portion of the sacrificial thermal oxide layer 104, is formed below the edge of a power portion of the mask pattern 102.

Referring to FIG. 4A, FIG. 4B, and FIG. 4C, using the mask pattern 102 as an etch mask, the thermal oxide layer 104 and the substrate 100 are successively anisotropically etched to form a fin 106 protruding upwardly on the substrate 100. Due to the bird's beak 105, an upper corner of the fin 106 is rounded. The bird's beak 105 may remain even after the etch process for forming the fin 106 is finished. To cure the etch damage of the fin 106, a thermal oxidation process may be carried out to form a sidewall thermal oxide layer (not shown).

A filling insulation layer is formed on the entire surface of the substrate 100. The filling insulation layer is planarized until the mask pattern 102 is exposed. The planarized filling insulation layer is recessed to form a filling insulation pattern 108 surrounding a lower sidewall of the fin 102. The mask pattern 102 and the remaining bird's beak 105 are removed to expose both sidewalls and the top surface of an upper portion of the fin 106. The bird's beak 105 may be removed when the planarized filling insulation layer is recessed. Alternatively, the bird's beak 105 may be removed by a process of removing the mask pattern 102 or an additional removal process. In some exemplary embodiments, the filling insulation pattern 108 may be formed following removal of the mask pattern 102. The filling insulation pattern 108 may be made of an insulation material having a superior gap-fill property, for example, high-density plasma oxide or SOG.

A first insulation layer 110 is formed on the exposed surface of the fin 106 (i.e., a top surface and an upper sidewall of the fin 106). Preferably, the first insulation layer 110 is made of thermal oxide. A first storage layer 112 is formed on the entire surface of the substrate 100 to fill the etched portion of the substrate 100. A top surface of the first storage layer 112 may be planarized. Preferably, the first storage layer 112 is made of first doped polysilicon.

Referring to FIG. 5A, FIG. 5B, and FIG. 5C, the first storage layer 112 is planarized until the first insulation layer 110 disposed on the top surface of the fin 106 is exposed. The planarization process may be done using chemical mechanical polishing (CMP) or etch-back. The planarized first storage layer 112 a surrounds the sidewall of the fin 106 with the first insulation layer interposed therebetween. More specifically, the planarized first storage layer 112 a surrounds the upper sidewall of the fin 106 protruding upwardly on the filling insulation pattern 108.

Referring to FIG. 6A, FIG. 6B, and FIG. 6C, an oxidation barrier layer 114 is formed on the entire surface of the substrate 100. The oxidation barrier layer 114 is made of a material to prevent oxidation of the planarized first storage layer 112 a. Preferably, the oxidation barrier layer 114 is made of a material (e.g., silicon nitride or silicon oxynitride) having an etch selectivity with respect to the first insulation layer 110.

The oxidation barrier layer 114 is patterned to form an opening 116 exposing a predetermined area of the first insulation layer 110. The exposed first insulation layer 110 is disposed on the top surface of the fin 106. The area exposed by the opening 116 includes a horizontal channel region of a channel region and may be larger than the horizontal channel region to secure an align margin. Although FIG. 6B shows that a sidewall of the opening 116 is aligned to the planarized first storage layer 112 a, the opening 116 may expose a portion adjacent to the first insulation layer 110 of the planarized first storage layer 112 a.

Referring to FIG. 7A, FIG. 7B, and FIG. 7C, using the patterned oxidation barrier layer 114 as an etch mask, the exposed first insulation layer 110 is removed to expose the top surface of the fin 106.

The substrate 100 is then thermally oxidized to form a second insulation layer 118 on the exposed top surface of the fin 106. The second insulation layer 118 is thinner than the first insulation layer 110. At a write or erase operation, the second insulation layer 118 is preferably thin enough to allow tunneling of charges. In contrast, at a write or erase operation, the first insulation layer 110 is preferably thick enough to suppress tunneling of charges. Accordingly, the second insulation layer 118 corresponds to a tunnel insulation layer.

Referring to FIG. 8A, FIG. 8B, and FIG. 8C, the patterned oxidation barrier layer 114 is removed from the substrate 100 to expose the planarized first storage layer 112 a. A second storage layer 120 is formed on the entire surface of the substrate 100. The second storage layer 120 covers the second insulation layer 118 and is electrically connected to the planarized first storage layer 112 a. Preferably, the second storage layer 120 is made of second doped polysilicon.

Preferably, the first polysilicon of the planarized first storage layer 112 a and the second polysilicon of the second storage layer are doped with impurities of the same type to achieve their electric connection. But their impurity concentrations are different from each other. Particularly, the impurity concentration of the first doped polysilicon is preferably higher than that of the second doped polysilicon.

By the foregoing, a contact surface of the second storage layer 120 and the planarized first storage layer 112 a (i.e., the top surface of the planarized first storage layer 112 a) may be taller than the top surface of the fin 106.

Referring to FIG. 2A, FIG. 2B, FIG. 2C, FIG. 9A, FIG. 9B, and FIG. 9C, the second storage layer 120 and the planarized first storage layer 112 a are successively patterned to form a second storage pattern 120 a and a first storage pattern 112 b. The first storage pattern 112 b surrounds the sidewall of the fin 106 with the first insulation layer 110 interposed therebetween. The second storage pattern 120 a covers the top surface of the fin 106 with the second insulation layer 118 interposed therebetween and is electrically connected to the first storage pattern 112 b. The first and second storage patterns 112 b and 120 a constitute a preliminary floating gate 122 that is disposed in parallel with the fin 106.

Although not shown in these figures, in the case where the opening 116 exposes a portion of the planarized first storage layer 112 a adjacent to the first insulation layer 110, the second insulation layer 118 may be formed on a portion of the first storage layer 112 a. In this case, only a portion of the top surface of the first storage pattern 112 b is connected to the second storage pattern 120 a.

A blocking insulation layer 124 is conformally formed on the entire surface of a substrate 100 including the preliminary floating gate 122. The blocking insulation layer 124 may be oxide-nitride-oxide (ONO). Alternatively, the blocking insulation layer 124 may be a high-k dielectric substance having a higher dielectric constant than silicon nitride. The blocking insulation layer 124 may be made of metal oxide such as, for example, aluminum oxide or hafnium oxide.

A control gate conductive layer 126 is formed on the blocking insulation layer 124. The control gate conductive layer 126 may be made of, for example, one selected from the group consisting of doped polysilicon (e.g., tungsten and molybdenum), conductive metal nitride (e.g., titanium nitride and tantalum nitride), metal silicide (e.g., tungsten silicide, cobalt silicide, nickel silicide and titanium silicide), and combinations thereof.

A capping insulation layer (not shown) may be formed on the control gate conductive layer 126. The capping insulation layer may be made of one selected from the consisting of silicon oxide, silicon nitride, silicon oxynitride, and combinations thereof.

The control gate conductive layer 126, the blocking insulation layer 124, and the preliminary floating gate 122 are successively patterned to form a floating gate 122 a, a blocking insulation layer 124, and a control gate electrode 126 a, which are illustrated in FIG. 2A, FIG. 2B, and FIG. 2C. The floating gate 122 a includes a first storage gate 112 a and a second storage gate 120 b. The first storage gate 112 a covers a sidewall of the fin 106 with the first insulation layer 110 interposed therebetween, and the second storage gate 120 b covers a top surface of the fin 106 with the second insulation layer 118 interposed therebetween and is connected to the first storage gate 112 c. The first and second storage gates 112 c and 120 b are formed from the first and second storage patterns 112 b and 120 a, respectively.

Using the control gate electrode 126 a as a mask, impurities are implanted to form an impurity doping layer 128 illustrated in FIG. 2C. The first insulation layer 110 and/or the second insulation layer 118 formed the surface of the fin 106 disposed at opposite sides adjacent to the control gate electrode 126 a may be removed before or after formation of the impurity doping layer 128.

The non-volatile memory device may have the effects that are described with reference to FIG. 2A, FIG. 2B, and FIG. 2C. That is, a channel region is defined at opposite sides and a top surface of the fin 106 below a control gate electrode 126 a to increase the width of the channel region within a limited area. Thus, the turn-on current of the non-volatile memory cell increases. Further, the first insulation layer 110 is thicker than the second insulation layer 118, so that the capacitance between the first storage gate 112 c and the fin 106 decreases. On the other hand, an overlap area of the control gate electrode 126 a and the floating gate 122 a of the 3-dimensional structure increases, so that their capacitance increases. As a result, the coupling ratio of the non-volatile memory cell increases. Since the first and second storage layers 112 and 120 are made of the first and second doped polysilicons that are sequentially formed, characteristics of the doped first and second polysilicons will be different. Particularly, since the impurity concentration of the doped first polysilicon is higher than that of the second doped polysilicon, a threshold voltage of the non-volatile memory cell may be uniformly achieved at the whole area of the channel region to enhance the operating speed of the non-volatile memory device.

Using another method, the second insulation layer 118 may selectively form on the top surface of the fin 106, which will be described with reference to FIG. 10A through FIG. 12A, FIG. 10B through FIG. 12B, and FIG. 10C through FIG. 12C.

FIG. 10A through FIG. 12A are top plan views for illustrating a method of selecting an insulation layer on the top surface of the fin, in the method of forming the non-volatile memory device according to an embodiment of the present invention. FIG. 10B through FIG. 12B are cross-sectional views taken along lines V-V′ of FIG. 10A through FIG. 12A, respectively. FIG. 10C through FIG. 12C are cross-sectional views taken along lines VI-VI′ of FIG. 10A through FIG. 12A, respectively.

In this method, exposing a first insulation layer 110 formed on a top surface of a fin 106 is performed by the same manner as previously described with reference to FIG. 3A through FIG. 5A, FIG. 3B through FIG. 5B, and FIG. 3C through FIG. 5C.

Referring to FIG. 5A, FIG. 5B, FIG. 5C, FIG. 10A, FIG. 10B, and FIG. 10C, recessed is a first storage layer 112 a that is planarized until a first insulation layer 110 disposed on a top surface of a fin 106 is exposed. The top surface of the recessed first storage layer 112 a′ is shorter than the top surface of the exposed first insulation layer 110. The top surface of the recessed first storage layer 112 a′ may be as tall as the top surface of the fin 106.

An oxidation barrier layer is formed on the entire surface of the substrate 100 to fill the recessed portion of the planarized first storage layer 112 a. The oxidation barrier layer is planarized until the first insulation layer 110 disposed on the top surface of the fin 106 is exposed. Thus, the planarized oxidation barrier layer 114′ is self-aligned to cover the recessed first storage layer 112 a′. The first insulation layer 110 formed on the top surface of the fin 106 is fully exposed. The oxidation barrier layer is made of the same material as the oxidation barrier layer 114 illustrated in FIG. 6A, FIG. 6B, and FIG. 6C.

Referring to FIG. 11A, FIG. 11B, and FIG. 11C, using the planarized oxidation barrier layer 114′ as the etch mask, the exposed first insulation layer 110 is etched to expose the whole top surface of the fin 106.

A thermal oxidation process is carried out to form a second insulation layer 118 on the exposed top surface of the fin 106. The second insulation layer 118 is formed on the entire top surface of the fin 106.

Referring to FIG. 12A, FIG. 12B, and FIG. 12C, the planarized oxidation barrier layer 114′ is removed from the substrate 100 to expose the top surface of the recessed first storage layer 112 a′. A second storage layer 120 is formed on the entire surface of the substrate 100 to cover the second insulation layer 118 and to electrically connect to the first storage layer 112 a′.

Subsequent processes may be carried out in the same manner as previously described with reference to FIG. 9A, FIG. 9B, and FIG. 9C. The subsequent processes include a process of successively patterning the second storage layer 120 and the recessed first storage layer 112 a′ to form a preliminary floating gate.

According to the above-described method, it is not necessary to perform a patterning process for forming an opening 116 described with reference to FIG. 6A, FIG. 6B, and FIG. 6C. The planarized oxidation barrier layer 114′ is formed on the first storage layer 112 a′ recessed by self-alignment. A boundary of the second storage layer 120 and the recessed first storage layer 112 a′ may be as tall as the top surface of the fin 106. A second storage gate 120 b of FIG. 2A, FIG. 2B, and FIG. 2C is in contact with an entire surface of a first storage gate 112 c.

The substrate mentioned in the foregoing embodiments is a bulk substrate. However, the non-volatile memory device may be formed on a silicon-on-insulator (SOI) substrate, which will now be described with reference to FIG. 13A and FIG. 13B. In this case, the filling insulation pattern 108 may not be required.

FIG. 13A is a cross-sectional view showing a modified version of the non-volatile memory device according to an embodiment of the present invention, and FIG. 13B is a cross-sectional view taken from a direction VII-VII′ of FIG. 13A.

Referring to FIG. 13A and FIG. 13B, a substrate 100′ includes a handling substrate 90 and a buried insulation layer 92 which are stacked in the order named. An upwardly protruding fin 106′ is disposed on the buried insulation layer 92. The fin 106′ includes a portion of a device layer of the substrate 100′ that is a SOI substrate. Preferably, an upper corner of the fin 106′ is rounded so as to prevent concentration of an electric field. A plan shape of the fin 106′ may be a line shape, as illustrated in FIG. 2A. The buried insulation layer 90 may serve to isolate the device and to electrically isolate the device from the handling substrate 90.

A control gate electrode 126 a is disposed to cross the fin 106′. A floating 122 a is interposed between the control gate electrode 126 a and the fin 106′. The floating gate 122 a includes a first storage gate 112 c and a second storage gate 120 b. A first insulation layer 110 is interposed between the first storage gate 112 c and a sidewall of the fin 106′. A second insulation layer 118 is interposed between the second storage gate 120 b and a top surface of the fin 106′. A blocking insulation pattern 124 a is interposed between the floating gate 122 a and the control gate electrode 126 a. An impurity doping layer 128 is disposed in the fin 106 on the opposite sides adjacent to the control gate electrode 126 a.

The first and second insulation layers 110 and 118, the floating gate 122 a, the control gate electrode 126 a, the blocking insulation pattern 124 a, and the impurity doping layer 128 may have the same characteristics as described above with reference to FIG. 2A, FIG. 2B, and FIG. 2C. Further, they may have the same shapes as illustrated in FIG. 2A.

The non-volatile memory device is disposed at the substrate 100′ which is a SOI substrate, obtaining the effects described with reference to FIG. 2A, FIG. 2B, and FIG. 2C and enhancing a leakage current characteristic. As a result, a non-volatile memory device of more reduced power consumption may be constructed.

A method of forming the foregoing non-volatile memory device on a SOI substrate will now be described below.

FIG. 14A and FIG. 15A are cross-sectional views for explaining a method of forming the modified version of the non-volatile memory device according to an embodiment of the present invention. FIG. 14B and FIG. 15B are cross-sectional views viewed from directions VIII-VIII′ of FIG. 14A and FIG. 15A, respectively.

Referring to FIG. 14A and FIG. 14B, a mask pattern 102 is formed on a predetermined region of a substrate 100′. The substrate 100′ is a SOI substrate including a handling substrate 90, a buried insulation layer 92, and a device layer which are stacked in the order named. As previously stated, the mask pattern 102 serves to prevent oxidation caused by the thermal oxidation process and has an etch selectivity with respect to the substrate 100′. Particularly, the mask pattern 102 has an etch selectivity with respect to the device layer 95. As described above, the mask pattern 102 may be a single layer made of silicon nitride or a multiple layer of silicon oxide/silicon nitride.

A substrate 100′ including the mask pattern 102 is thermally oxidized to form a sacrificial thermal oxide layer 104. A bird's beak 105, which is an extending portion of the sacrificial thermal oxide layer 104, is formed below the edge of a bottom surface of the mask pattern 102.

Referring to FIG. 15A and FIG. 15B, using the mask pattern 102 as an etch mask, the sacrificial thermal oxide layer 104 and the device layer 95 of the substrate 100′ are successively isotropically etched to form an upwardly protruding fin 106′ on the substrate 100′. The fin 106′ is formed on the buried insulation layer 92 of the substrate 100′. Undoubtedly, an upper corner of the fin 106′ is rounded by the bird's beak 105. As previously stated, a thermal oxidation process may be carried out to cure the etch damage of the fin 106′.

A first insulation layer 110 is formed on the surface of the fin 106′. A first storage layer 112 is formed on the first insulation layer 110 to fill an etched portion of the substrate 100′. The first insulation layer 110 and the first storage layer 112 are the same as described above and will not be described in further detail.

Subsequent processes following formation of the first storage layer 112 may be carried out in the same manner as described with reference to FIG. 5A through FIG. 9A, FIG. 5B through FIG. 9B, and FIG. 5C through FIG. 9C. Alternatively, subsequent processes following the formation of the first storage 112 may be carried out in the same manner as described with reference to FIG. 10A through FIG. 12A, FIG. 10B through FIG. 12B, and FIG. 10C through FIG. 12C.

Other modifications and variations to the invention will be apparent to a person skilled in the art from the foregoing disclosure. Thus, while embodiments of the invention have been specifically described herein, it will be apparent that numerous modifications may be made thereto without departing from the spirit and scope of the invention. 

1. A non-volatile memory device comprising: an upwardly protruding fin disposed on a substrate; a control gate electrode crossing the fin; a floating gate including a first storage gate and a second storage gate interposed between the control gate and the fin, the first storage gate disposed on a sidewall of the fin, and the second storage gate being disposed on a top surface of the fin and connected to the first storage gate; a first insulation layer and a second insulation layer, the first insulation layer interposed between the first storage gate and the sidewall of the fin, and the second insulation layer is thicker than the first insulation layer and interposed between the second storage gate and the top surface of the fin; and a blocking insulation layer interposed between the control gate electrode and the floating gate.
 2. The non-volatile memory device as recited in claim 1, wherein the first storage gate is made of a first doped polysilicon, and the second storage gate is made of a second doped polysilicon.
 3. The non-volatile memory device as recited in claim 2, wherein an impurity concentration of the first doped polysilicon is different from that of the second doped polysilicon.
 4. The non-volatile memory device as recited in claim 3, wherein the impurity concentration of the first doped polysilicon is higher than that of the second doped polysilicon.
 5. The non-volatile memory device as recited in claim 1, wherein at a write or erase operation, the second insulation layer has a thickness sufficient to allow tunneling of charges and the first insulation layer has a thickness sufficient to suppress tunneling of charges.
 6. The non-volatile memory device as recited in claim 1, wherein an upper corner of the fin is rounded.
 7. The non-volatile memory device as recited in claim 1, wherein the first and second insulation layers are made of thermal oxide.
 8. The non-volatile memory device as recited in claim 1, wherein an outer sidewall of the first storage gate is aligned to a sidewall of the second storage gate.
 9. The non-volatile memory device as recited in claim 1, further comprising a filling insulation pattern disposed on the substrate to surround a lower sidewall of the fin.
 10. The non-volatile memory device as recited in claim 1, further comprising a buried insulation layer disposed on the substrate, the fin being disposed on the buried insulation layer.
 11. A method of forming a non-volatile memory device, comprising: forming an upwardly protruding fin on a substrate; sequentially stacking a first insulation layer and a first storage pattern on a sidewall of the fin; sequentially stacking a second insulation layer and a second storage pattern on a top surface of the fin, the second insulation layer being thinner than the first insulation layer and the second storage pattern being connected to the first storage pattern; sequentially forming a blocking insulation layer and a control gate conductive layer on the substrate; and successively patterning the control gate conductive layer, the blocking insulation layer, the first storage pattern, and the second storage pattern to form a floating gate including a first storage gate and a second storage gate, a blocking insulation pattern, and a control gate electrode.
 12. The method as recited in claim 11, wherein the first storage gate is made of a first doped polysilicon, and the second storage gate is made of a second doped polysilicon.
 13. The method as recited in claim 12, wherein an impurity concentration of the first doped polysilicon is different from that of the second doped polysilicon.
 14. The method as recited in claim 13, wherein the impurity concentration of the first doped polysilicon is higher than that of the second doped polysilicon.
 15. The method as recited in claim 11, wherein forming the first insulation layer, the first storage pattern, the second insulation layer, and the second storage pattern comprises: forming a first insulation layer on a top surface and a sidewall of the fin; forming a first storage layer surrounding the sidewall of the fin on the first insulation layer to expose the first insulation layer formed on the top surface of the fin; selectively removing the exposed first insulation layer to expose the top surface of the fin; selectively forming a second insulation layer on the top surface of the exposed fin; forming a second storage layer to cover the second insulation layer and to be connected to the first storage layer; and successively patterning the second and first storage layers to form the second and first storage patterns.
 16. The method as recited in claim 15, wherein exposing the top surface of the fin and forming the second insulation layer comprise: forming an oxidation barrier layer on an entire surface of a substrate including the exposed first insulation layer; patterning the oxidation barrier layer to expose a predetermined region of the exposed first insulation layer; using the patterned oxidation barrier layer as an etch mask, etching the first insulation layer to expose the top surface of the fin; thermally oxidizing the substrate to form the second insulation layer; and removing the patterned oxidation barrier layer.
 17. The method as recited in claim 16, wherein at a write or erase operation, the second insulation layer has a thickness sufficient to allow tunneling of charges and the first insulation layer has a thickness sufficient to suppress tunneling of charges.
 18. The method as recited in claim 16, wherein an upper corner of the fin is rounded.
 19. The method as recited in claim 18, wherein forming the fin comprises: forming a mask pattern on a predetermined region of a substrate; thermally oxidizing a substrate including the mask pattern to form a sacrificial thermal oxide layer including a bird's beak below the edge of a lower side of the mask pattern; using the mask pattern as an etch mask, successively anisotropically etching the sacrificial thermal oxide layer and the substrate to form the fin; and removing the mask pattern and the bird's beak, wherein the upper corner of the fin is rounded by the bird's beak.
 20. The method as recited in claim 15, wherein exposing the top surface of the fin and forming the second insulation layer comprise: recessing the first storage layer to be shorter than a top surface of the exposed first insulation layer; forming an oxidation barrier layer on a substrate to fill the recessed region; planarizing the oxidation barrier layer until the first insulation layer is exposed; using the planarized oxidation barrier layer as an etch mask, etching the exposed first insulation layer to expose the top surface of the fin; thermally oxidizing the substrate to form the second insulation layer; and removing the planarized oxidation barrier layer.
 21. The method as recited in claim 20, wherein at a write or erase operation, the second insulation layer has a thickness sufficient to allow tunneling of charges and the first insulation layer has a thickness sufficient to suppress tunneling of charges.
 22. The method as recited in claim 20, wherein the upper corner of the fin is rounded.
 23. The method as recited in claim 22, wherein forming the fin comprises: forming a mask pattern on a predetermined region of a substrate; thermally oxidizing a substrate including the mask pattern to form a sacrificial thermal oxide layer including a bird's beak below the edge of a lower side of the mask pattern; using the mask pattern as an etch mask, successively anisotropically etching the sacrificial thermal oxide layer and the substrate to form the fin; and removing the mask pattern and the bird's beak, wherein the upper corner of the fin is rounded by the bird's beak.
 24. The method as recited in claim 11, further comprising forming a filling insulation pattern on the substrate to surround a lower sidewall of the fin.
 25. The method as recited in claim 11, wherein the substrate is a SOI substrate including a handling substrate, a buried insulation layer, and a device layer which are sequentially stacked and the step of forming the fin includes patterning the device layer to form an upwardly protruding fin on the buried insulation layer. 